1. Field of the Invention
In general, the invention relates to pneumatic dust hoods, and more specifically to pneumatic hoods for capturing dust in paper and tissue manufacturing processes.
2. Description of Related Art
Modern industrial tissue-making processes are typically performed using a single machine. On the “wet” side of the machine, a combination of plant fibers, typically some combination of virgin and recycled wood pulp is formed by pressing between a wire mesh and a felt as it wraps around a forming roll. The wet web is transferred to a large-diameter drying cylinder, called a yankee cylinder, and is peeled from the yankee cylinder by a scraping blade, called a doctor blade. As the web winds through the “dry” side of the machine, it passes through a maze of turns, is calendered (i.e., softened by compressing the web) and may go through a slitting process before being wound into a final roll, called a parent roll. The tissue on the parent roll may be further processed, depending on the product that is being made.
Tissue-making machines are often very large—the machine itself may be 5.7 or 2.4 meters wide with a tissue web very nearly that wide—and operate at very high speeds, e.g., of up to 2,000 meters per minute. The speed of the machine and the volume of paper that passes through in a short period of time create a large volume of paper particles and dust. The dust is a health hazard for workers, and if it builds up enough, it can also be an explosion hazard. Beyond that, accumulated dust and paper can impede the web of tissue and require the machine to be shut down in order to clear clumps and accumulations.
In order to prevent dust accumulation, dust extraction hoods are typically placed at strategic locations, especially along the “dry” side of the machine. However, these hoods face potential issues. For example, while much of the maculature or detritus is in the form of dust and small particles, larger clumps and pieces of paper can form. For example, because the machine operates at such high speed, breakage of the paper web is not uncommon, and if the web breaks, the shredded tails of the web, and other, larger pieces of paper, can be thrown off at high velocity and drawn into the hoods. These larger clumps can cause a loss of hood efficiency and may require the hood (and potentially also the papermaking machine itself) to be shut down while the blockage is cleared.